Shipping container blanks encapsulated in plastic film

ABSTRACT

The invention is a shipping container blank whereby all surfaces and edges are sealed by an overlying a plastic film material. A container subsequently made from the blank is rendered highly water resistant. The film material is applied to both sides of the blank and severed from the supply source. The covered blank is then heated above the softening point of the film. The film becomes bonded to the surfaces of the blank and sags around the edges and into any openings so that the film on the two sides of the blank come into contact and are sealed to each other. The edges and any slits and cutouts are then trimmed, as by a die cutter, while preserving the seals along the edges. Containers made by the process can generally be recycled, in contrast to wax or resin impregnated corrugated board.

[0001] This application is a continuation of application Ser. No.09/449,259, filed Nov. 24, 1999, and now U.S. Pat. No.

[0002] The present invention is directed to a method of overlaying aplastic film material on a shipping container blank, to the highly waterresistant blank formed by the method, and to a container subsequentlyformed from the blank.

BACKGROUND OF THE INVENTION

[0003] Water resistant shipping containers are required for shippingmany types of fresh produce. Containers used to date have principallybeen prepared by saturating the blank with melted wax before assembly.Other methods have included impregnation with a water resistantsynthetic resin or coating the container with a thermoplastic material.In the latter case, forming watertight seals around the edges and anyslits or openings has been a major problem. In most cases the resultingcontainers cannot be recycled and must be disposed of in a landfill.

[0004] One early method of plastic coating is seen in Peters, U.S. Pat.No. 3,406,052 where plastic material is applied by extruders depositinga thin film against both faces of a moving box blank. The extruded filmis wider than the blank so that it hangs over all edges. These are thensealed with a flame. Alternatively, the edges of the blank may becrushed and sealed with a thermoplastic mixture. No provision was madefor sealing any openings other than the edges.

[0005] Marshall, in U.S. Pat. No. 3,864,200, describes a box made usingresin impregnated linerboards and a two layer corrugated medium havingan asphalt barrier coating between the layers. All exposed edges arecrushed for a width of about 0.5-1 inch and the asphalt bleeds throughthe corrugated medium to provide some sealing.

[0006] Maughan, in U.S. Pat. No. 3,929,536, shows a moisture resistantcorner post usable in packaging materials. This is made from multiplelayers of corrugated paperboard fully enclosed in a plastic film. Avacuum former preferably is used to bring the heated shrink wrap plasticfilm into conformation. End seals are made by an undisclosed method.

[0007] Inagaki discloses in U.S. Pat. No. 4,551,123 a tubular papercontainer sealed within a thermoplastic film. Edges are either plasticwrapped or heat sealed.

[0008] Dropsy, in U.S. Pat. No. 4,722,474 shows a package with aninternal thermoformed seam free plastic liner. One embodiment also showsa plastic coated outer surface with the outer and inner films being heatsealed along the edges. The plastic coating is apparently applied afterformation of the container. French Patent No. 2,645,831 is closelyrelated.

[0009] WO 94/02364 describes a container blank formed entirely of acorrugated of thermoplastic material. Edges and all other openings aresealed to add strength and prevent entry of liquid.

[0010] WO 90/09927 shows a thermoplastic film encapsulated shippingcontainer blank similar to one made by the process of the presentinvention. A plastic film is applied to both sides of a corrugatedshipping container blank and subsequently heat sealed around all edgesand openings. The document is strangely silent in regard to any processsteps by which the encapsulated container blank is prepared.

[0011] The present invention describes an efficient process by which aplastic encapsulated corrugated shipping container blank may be formed.

SUMMARY OF THE INVENTION

[0012] The present invention is directed to a method of fullyencapsulating corrugated shipping container blanks within a moistureresistant plastic film. The method requires a source of thin,thermobondable, thermoplastic film. This is applied to both sides of acontainer blank. At a downstream location the film is heated on bothsides of the blank to a sufficient temperature so that the film bonds tothe blank without additional adhesive. The opposing film layers sag tocontact each other along the edges and over the area of any openings andare thermobonded to form seals. After a brief cooling period, excessfilm along the edges and within any openings is die cut or otherwiseremoved, leaving the sealed edges intact.

[0013] Most preferably, the film is applied as a sleeve wrap in whichfilm supply rolls are located above and below a conveyor system, theaxes of the rolls being transverse to the direction of travel on theconveyor. The film from each supply roll spans a planar intermediatespace perpendicular to the conveyor travel direction and is thermallybonded end-to end to form a continuous sheet. A container blank movingalong the conveyor contacts the film and draws it from the rolls as ittravels forward. The film is directed into contact against the upper andlower faces of the container blank by rolls or a similar arrangement.When the container blank has passed the planar intermediate location thefilm at the trailing edge of the container blank is pinched together andthermally bonded. This provides fore and aft seals of the film wrap. Thefilm at the location of this thermal bond is severed transversely sothat the seal remains intact on both sides of the severing line. Thewrapped container blank continues down the conveyor line and the filmfrom the supply rolls is again bonded together end-to-end, ready to beengaged by the following container blank. A heating station follows inwhich the film is bonded to the container blank. At this point the filmsags into any slits and other openings and the upper and lower films arebonded together where in contact with each other. Some shrinkage of thefilm occurs at this time causing the seals to contract tightly againstany exposed edges. A die cutter opens the slits and cutouts whilekeeping the seals intact. The container blank is now fully encapsulatedwith continuous seals around the peripheral edges and corner slits orother cutout portions and is ready to be formed into a moistureresistant shipping container.

[0014] The container when so encapsulated can be readily recycled sincethe film is easily removed in a repulper and can be readily separatedfrom the fiber portion in conventional fiber cleaning equipment..

[0015] It is an object of the invention to provide a method forpreparing a highly moisture resistant shipping container.

[0016] It is a further object to prepare a moisture resistant shippingcontainer that can be readily recycled.

[0017] These and many other objects will become readily apparent uponreading the following detailed description taken in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 shows a plastic encapsulated corrugated paperboard boxblank ready to be formed into a ventilated shipping container.

[0019]FIG. 2 diagramatically illustrates the process of encapsulating acontainer blank within a plastic film

[0020]FIG. 3 is a section through line 3-3 of FIG. 1

[0021]FIG. 4 is a portion in cross section showing greater detail of theedge seal of the plastic coating.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The thermoplastic, thermobondable plastic film used in thepresent method may be a single layer film but is preferably a multilayerfilm comprising at least first and second layers. When a two layer filmis used the layers should have a melting point difference of at leastabout 15° C. (25°-30° F.). Most typically the film will be a coextrudedfilm having an outer layer of high density polyethylene with a meltingpoint of about 130° C. (265°-275° F.) and an inner layer with a meltingpoint of about 110° C. (230°-240° F.). The inner layer is used adjacentto and is thermobondable to the corrugated paper shipping containerblank. A most preferred film is a coextruded film as just described witha third metallocene composition adjacent the low density polyethylenelayer to promote good adhesion to the container blank surface. A film ofthis type is available from Golden Eagle Extrusions Inc., Loveland,Ohio, and from other suppliers. Other film compositions such as thosebased on polypropylene, poly(vinyl chloride), polyesters, or filmshaving one or more layers of one of these compositions coextruded withone of the other compositions. Film thickness is not critical but willgenerally be within the range of about 0.019-0.075 mm (0.00075-0.003in). Most typically the film will be about 0.025 mm (0.001 in) inthickness.

[0023] The film may be applied to each side of the shipping containerblank by any method. Most preferably it is applied by the sleeve wrapmethod described earlier.

[0024] In addition to providing a highly water resistant container, thepresent method can provide a product that is significantly superior inappearance to conventional printed containerboard blanks. This isaccomplished by using a pigmented film on at least the outer surface ofthe ultimate shipping container. The pigmented film can be printedbefore or after application to the container blank. Image brightness andclarity is outstanding in comparison to that usually seen on printedcontainerboard conventionally made using an outer linerboard ply havingan integrally formed thin white surface layer.

[0025] The method by which the product is prepared is best understood byreference to the drawings. FIG. 1 represents a completed containerboardblank 2 having side walls 4, end walls 6, and top and bottom flaps 8,10. A single flap 12 is provided to make the manufacturers joint whenthe container is assembled. Cutouts 14, and score lines 15 are providedto facilitate assembly. The entire upper and lower surfaces are coveredwith a plastic film 18 with the two layers sealed to each other alongthe edges and at all openings.

[0026] A preferred method of forming the product is seen in FIG. 2. Acontainer blank 20 is fed into a sleeve wrap station where plastic filmis supplied from upper and lower rolls, not shown. The container blankmoves along a conveyer and withdraws the film from the supply rolls asit moves forward. The film is pressed against the container blank andthen heat sealed and severed at the trailing edge. Film from the twosupply rolls is reunited by the heat seal and is ready to receive thefollowing container blank. A heating station 24 bonds the film to thecontainer blank. As shown here, heated rolls 26 perform this functionbut other heating means, such as infra red or a heated press, can beequally suitable. During heat application at station 24 the film isheated on both sides so that is softened to the point where it sags intoall openings, such as slits 14 and cutouts 16, and around all of theperipheral edges. At the sag locations the upper and lower films contactand bond to each other as is best seen in FIG. 3.

[0027]FIG. 3 shows a cross section along line 3-3 of FIG. 1. Thecontainer blank 20 has upper and lower paper linerboards 40 bonded to aninterior corrugated medium 42. The linerboards are overlaid with plasticfilms 44. As shown, the film sags into the score lines 46 and into thecutout openings 48. The two films meet and form bonds 50 at the edgesand 52 at cutout locations 48. FIG. 4 shows an enlarged view at one ofthe cutout locations. Here, the film bridging the cutout serving as aventilation opening has been removed by a die cutter leaving the edgebonds 52.

[0028] It will be evident to those skilled in the art that manyvariations can be made in the described process without departing fromthe spirit of the invention. It is the inventors intent that thesevariations should be included within the scope of the invention ifencompassed within the following claims.

We claim:
 1. A moisture resistant corrugated shipping container blankwhich comprises a corrugated paper shipping container blank completelyencapsulated within a thermoplastic film, said blank having slits forforming the blank into a container and cutouts providing ventilation forthe container contents, the plastic film completely enclosing allexposed edges of the blank and the edges of the slits and cutouts inorder to prevent moisture entry, the slits and cutouts being open withthe seals around their edges remaining intact.
 2. The shipping containerblank of claim 1 in which the thermoplastic film comprises at leastfirst and second layers, said layers having a difference in meltingpoints of at least about 15° C., said first layer having the lowermelting point and being located adjacent the shipping container blank 3.The shipping container blank of claim 2 in which the lower melting pointlayer has a melting point of at least about 110° C. and the second layerhas a melting point of at least about 130° C.
 4. The shipping containerblank of claim 1 in which the plastic film has a thickness of about0.019-0.075 mm (0.00075-0.003 inches).
 5. The shipping container blankof claim 2 in which the plastic film has a thickness of about0.019-0.075 mm (0.00075-0.003 inches).
 6. The shipping container blankof claim 1 in which the plastic film is a coextruded multi-layer filmhaving at least one layer of high density polyethylene and one of lowdensity polyethylene, the low density layer being located closest to theshipping container blank.
 7. The shipping container blank of claim 2 inwhich the plastic film is a coextruded multi-layer film having at leastone layer of high density polyethylene and one of low densitypolyethylene, the low density layer being located closest to theshipping container blank.
 8. The shipping container blank of claim 1 inwhich the film is pigmented.
 9. The shipping container of claim 10 inwhich the film is printed before or after application to the shippingcontainer blank.
 10. A shipping container formed from the blank of claim1.